Physiology, Glucose Transporter Type 4 (GLUT4)

Article Author:
Elizabeth Vargas

Article Editor:
Maria Alicia Carrillo Sepulveda

Editors In Chief:
Linda Lindsay

Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Frank Smeeks
Kristina Soman-Faulkner
Trevor Nezwek
Radia Jamil
Patrick Le
Sobhan Daneshfar
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Pritesh Sheth
Hassam Zulfiqar
Navid Mahabadi
Steve Bhimji
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Mark Pellegrini
James Hughes
Beata Beatty
Nazia Sadiq
Hajira Basit
Phillip Hynes
Tehmina Warsi

1/8/2019 11:34:17 PM


Among the numerous homeostatic events maintained by the human body, the blood glucose level is a significant physiologic aspect under persistent tight regulation.  Glucose is an essential energy source that requires careful regulation within the body as both too much or too little glucose can cause detrimental effects. Blood glucose level is impacted by carbohydrate ingestion and regulated by insulin. Insulin regulates peripheral glucose uptake and glucose production within the liver — a family of five transmembrane proteins, known as GLUT, transport glucose via facilitated diffusion across the cell plasma membrane. They differ in kinetics and tissue distribution.  The primary regulatory mechanism by which glucose uptake takes place is via insulin-stimulated transport of glucose into skeletal muscle and adipose tissue, primarily mediated by glucose transporter protein type-4 (GLUT4). GLUT4 is a key component in glucose homeostasis and the removal of glucose from circulation.[1][2]


GLUT4 is part of a family of glucose transporter proteins containing 12-transmembrane domains.  It is expressed primarily in skeletal muscle and adipose tissue. Unique N-terminal and COOH-terminal sequences are responsible for GLUT4’s responsiveness to insulin signaling and membrane trafficking.  The transportation of glucose across the cell membrane occurs via GLUT4’s mechanism of ATP-independent facilitative diffusion. Once glucose influxes into the cell, it can be metabolized for energy or lipid synthesis, or stored as glycogen.[1]

GLUT4 shifts its location between the intracellular domain and the plasma membrane.  By being part of an intracellular tubulo-vesicular network connected to the endosomal-trans-Golgi network (TGN) system, it is able to switch locations based on the presence of stimulation.  In the absence of insulin or exercise, 90% of GLUT4 remains intracellular. In the presence of insulin or exercise, GLUT4 storage vesicles undergo exocytosis to the plasma membrane, as well as the sarcolemma and T-tubules of skeletal muscle cells, where it can carry out its function on glucose transport.  This increase in the number of GLUT4 molecules available at the cell surface increases the maximal velocity of glucose transport rate into cells. Once there is the removal of insulin stimulation, GLUT4 is endocytosis back into the cell by budding of vesicles on the plasma membrane containing clathrin. Upon internalization, GLUT4 becomes a part of early endosomes and re-sorted back into intracellular vesicles.[3][2]


GLUT4 exists in skeletal muscle cells, adipocytes, and cardiomyocytes.  It is principally responsible for insulin-stimulated glucose uptake into muscle and adipose cells.  Approximately 80% of glucose gets transported into muscle cells. GLUT4’s glucose-transport system can be upregulated to meet elevated transport demands, such as during times of elevated blood glucose during a carbohydrate-containing meal, or during exercise when skeletal muscles have increased metabolic demand.[3]


Insulin-Mediated Stimulation

Insulin-regulated GLUT4 translocation can occur by two signaling pathways.  One pathway involves lipid kinase phosphatidylinositol 3-kinase (PI3K). Insulin binds to the insulin receptor found on the target cell surface, causing the receptor to undergo a conformational change which activates its tyrosine-kinase domain intracellularly.  Insulin receptor substrates (IRS) and c-Cbl (a proto-oncoprotein) are then phosphorylated. In muscle and adipose cells, IRS-1 and IRS-2 are the most important substrates. These substrates are located near the plasma membrane and recruit effector molecules to the area, such as PI3K which has been shown to take part in GLUT4 translocation to the plasma membrane.[3]

The other pathway involves proto-oncoprotein c-Cbl.  Insulin stimulates a dimeric complex of c-Cbl and c-Cbl associated protein (CAP) to move into lipid rafts on the cell surface.  Phosphorylation of c-Cbl recruits to the lipid rafts an adaptor protein complex (CrkII) and an exchange factor (C3G) for GTPase TC10.  TC10 specifically localizes to lipid rafts. Thus, activation of TC10 by C3G is an insulin-dependent process which subsequently translocated GLUT4.  If this pathway gets inhibited, inhibition will likewise occur for insulin-stimulated GLUT4 translocation in adipocytes.[3][4]

Non-Insulin Mediated Stimulation

Physical activity stimulates GLUT4 translocation to the plasma membrane in skeletal muscle.  This stimulation occurs via a mechanism independent from PI3K, which is necessary for the insulin-stimulated pathway.  Skeletal muscle contraction activates 5’-AMP-activated protein kinase (AMPK) which is believed to translocate exercise-responsive GLUT4-containing vesicles to the cell surface to mediate glucose transport; this occurs to meet the increased energy demands of skeletal muscle during exercise.[2][3]

Clinical Significance

Type 2 diabetes mellitus (T2DM) has increased dramatically over the years and continues to do so at an alarming rate.  It is a disease characterized by insulin resistance, meaning the insulin produced by the body is not enough to meet the glucose transport demands, leading to an elevated amount of glucose remaining in the body’s circulating plasma.  This chronic state of hyperglycemia can lead to a multitude of long-term complications, such as retinopathy, neuropathy, renal disease, and most lethally - heart disease. Insulin resistance has also been found to be a key component in obesity and metabolic syndrome (insulin resistance, dyslipidemia, and hypertension).  GLUT4 expression is severely disrupted in individuals with T2DM and heavily contributes to insulin resistance disease pathophysiology as it obstructs glucose transport from extracellular to intracellular uptake for storage and metabolism. Potential causes for resistance to insulin-stimulated glucose transport may be because of defective intracellular signaling of GLUT4 translocation in skeletal muscle from stored intracellular vesicles to active components of the plasma membrane, which may be due to an inherent impairment in the muscle cells as T2DM is a heritable disease. It may also be due to glucose toxicity from chronic hyperglycemia, or elevated levels of free fatty acids or TNF-alpha in the serum.  As a result of GLUT4 expression downregulation, adipocytes also exhibit impaired insulin-stimulated glucose uptake.[3][2]

Research shows that increasing intracellular concentrations of GLUT4 can improve or even reverse T2DM.  A non-pharmacological method of doing so is by incorporating exercise into an individual’s lifestyle. Skeletal muscle contractions activate exercise-responsive GLUT4-containing vesicles for exocytosis to the cell surface via a mechanism that functions independently from that of the insulin-stimulated pathway.  Individuals at high risk of developing T2DM may decrease their risk by regularly incorporating exercise into their routine. One study found that females who exercised at least once per week had a 33% decrease in the risk of developing T2DM than sedentary women.[2][5]

From a pharmacologic standpoint, drugs such as metformin,  thiazolidinediones, and sulfonylureas may be used to ameliorate glycemic control in T2DM individuals.   Sulfonylureas stimulate the release of insulin from pancreatic beta cells by inhibiting potassium-channels responsible for insulin uptake into the cell, thus blocking this process increases insulin availability in the serum.  Metformin is a biguanide which functions to primarily decrease hepatic glucose production, as well as decrease intestinal glucose absorption. Thiazolidinediones improve insulin sensitivity by inhibiting a nuclear receptor primarily in adipocytes, known as peroxisome proliferator-activated receptor (PPAR-gamma) which alters gene transcription involving glucose and fat metabolism.  Part of its mechanism of action is that it improves GLUT4 translocation by decreasing the level of TNF-alpha.[2][6][7][8]

Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Physiology, Glucose Transporter Type 4 (GLUT4) - Questions

Take a quiz of the questions on this article.

Take Quiz
A 58-year-old male with newly diagnosed type 2 diabetes mellitus presents to discuss management options. The patient is informed that along with various pharmacologic options, incorporating exercise into his routine can significantly aid in maintaining a normal blood glucose level. On a cellular level, what effect does exercise have to aid in blood glucose level homeostasis?

Click Your Answer Below

Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.

Sign Up

Physiology, Glucose Transporter Type 4 (GLUT4) - References


Huang S,Czech MP, The GLUT4 glucose transporter. Cell metabolism. 2007 Apr     [PubMed]
Bryant NJ,Govers R,James DE, Regulated transport of the glucose transporter GLUT4. Nature reviews. Molecular cell biology. 2002 Apr     [PubMed]
Watson RT,Kanzaki M,Pessin JE, Regulated membrane trafficking of the insulin-responsive glucose transporter 4 in adipocytes. Endocrine reviews. 2004 Apr;     [PubMed]
Shepherd PR,Kahn BB, Glucose transporters and insulin action--implications for insulin resistance and diabetes mellitus. The New England journal of medicine. 1999 Jul 22;     [PubMed]
Borghouts LB,Keizer HA, Exercise and insulin sensitivity: a review. International journal of sports medicine. 2000 Jan;     [PubMed]
Ashcroft FM, Mechanisms of the glycaemic effects of sulfonylureas. Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme. 1996 Sep;     [PubMed]
Pernicova I,Korbonits M, Metformin--mode of action and clinical implications for diabetes and cancer. Nature reviews. Endocrinology. 2014 Mar;     [PubMed]
Hauner H, The mode of action of thiazolidinediones. Diabetes/metabolism research and reviews. 2002 Mar-Apr;     [PubMed]


The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of NP-Advanced Physiology. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for NP-Advanced Physiology, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in NP-Advanced Physiology, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of NP-Advanced Physiology. When it is time for the NP-Advanced Physiology board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study NP-Advanced Physiology.